Off-peak train fares will rise 1% below inflation from 2016, the Scottish government has said.
The condition to peg off-peak fares at RPI -1, or 1% below the retail price index measure of inflation, will be written into the contract for the next rail franchise.
ScotRail said last week the cost of its tickets would rise by 3.9% in January.
But it pledged to freeze the price of off-peak fares in 2014 and 2015.
And the operator said peak fares would be capped at RPI in both years, so long as the annual rate remained below 3.5%.
Transport Minister Keith Brown said the Scottish government "recognises the financial pressures being faced by people every day and paying for their commute is part of that".
He added: "We are working hard to do all we can to ease that burden and helping keep rail fares down will not only be easier on the wallet but will also encourage more people to turn away from the ever-rising cost of the car, and let the train take the strain.
"We will ensure that peak fares can't rise above inflation, but today's announcement means we'll ensure off-peak tickets rise by even less. This will ensure an end to the incessant cycle of inflation-busting fares rises.
"I want to encourage greater rail use in the off-peak. I want attractive fares that will encourage commuters, where they can, to switch to off-peak services and better spread the demands on our rail services. I want families to use the train rather than the car for leisure travel. And I want greater use of sustainable travel. We all know it is better for our environment and our general well-being."
But Scottish Conservative transport spokesman Alex Johnstone questioned why it had taken Mr Brown "so long to peg the cost of off-peak rail fares and why he is determined to run such a rigid scheme."
He added: "He has to be more innovative in getting more people to use the trains away from peak times and would do well to look at how low cost airlines operate in order to reduce the number of empty seats on our rail network."
Labour's infrastructure spokesman, Richard Baker, said: "Yet again the promise is jam tomorrow from the SNP with a pledge on fares which will not come into effect until 2016.
"And yet again it is a pledge someone else will pay for - it is to be met by whoever runs the next franchise and we are not told how it will be funded or what impact it will have on rail services.
"Rather than make announcements on the next franchise in this piecemeal fashion, the minister should have a proper debate in parliament including into the possibility of the next franchise being run on a not-for-profit model."